Landslides in the Remolinos gypsum escarpment (NE Spain): controls imposed by stratigraphy, fluvial erosion, and interstratal salt dissolution

Abstract

Dissolution of karst rocks (evaporites and carbonates) can cause significant mechanical weakening, but its preparatory role for landslide development has been scarcely explored. Fluvial valleys carved in gypsum bedrock typically display prominent escarpments with numerous landslides and perched valleys indicative of rapid retreat rate. The stratigraphic and cartographic analysis of the 37-km-long Remolinos gypsum escarpment in the Ebro Valley (NE Spain) reveals that landslide types are controlled by the lithological succession: (1) rotational slides in sections with mudstones and marls at the base; (2) rock-slope collapses (massive rock-falls) where the cliff includes halite packages at the foot; and (3) relatively small rock-falls and topples being the main failures affecting cliffs entirely made by gypsum. Fluvial undercutting by the highly mobile Ebro River is the main process that controls the spatial and temporal distribution of slope instability. Geomorphic and chronological evidence supports that the abandonment in 1574 of the El Castellar village was at least partially motivated by a shift in the river channel toward the escarpment and the consequent landslide activity. Several lines of evidence support the concept whereby interstratal salt dissolution (halite and glauberite), here designated as subsurface solutional undermining, play a significant preparatory role for landslide development: (1) dissolution of salt close to the scarp by the inward advance of dissolution fronts and subsidence of the overlying strata; (2) collapsed fault blocks with no offset across the grabens; and (3) brine seepages and extensive efflorescences and precipitates of Na-sulfates and halite.